Potential Effects of Timber Harvest and Water Management on Streamflow Dynamics and Sediment Transport

The sustainability of aquatic and riparian ecological systems is strongly tied to the dynamics of the streamflow regime. Timber harvest can influence the flow regime by increasing total flow, altering peak discharge rate, and changing the duration of flows of differing frequency of occurrence. These changes in the energy and sediment transporting capability of the fluvial system can cause an alteration in both channel morphology and aquatic habitat. Depending on practices used, timber harvest can increase the rate of sediment introduction to the channel system, thus further confounding the energy/transport relationship. Diversion and augmentation also alter the natural flow regime and disrupt the energy distribution in the system. Diversion decreases the energy regime available to transport the sediment load and may cause aggradation and vegetation encroachment. Elevated flow regimes from augmentation may result in extensive scour, loss of aquatic habitat, and ultimately a change in the relationship between the aquatic and terrestrial components. This paper addresses the flow parameters which influence sediment transport and the implications of changing flow dynamics, whether from flow or forest management, and the effect it has on the transport process.